This invention relates generally to the field of valve actuation devices and systems for use with pressurized fluid containers. More particularly, it relates to an actuation system that provides automatic shut-off, under prescribed conditions, of a fluid flow control valve that is normally actuated manually.
Hazardous or toxic chemicals, such as, for example, chlorine and sulfur dioxide, are widely distributed in pressurized containers for use in water purification, sewage treatment, and a variety of industrial and agricultural applications. Many of these chemicals are immediately toxic to humans, even in very low concentrations. Accordingly, the containers, valves, and fittings, as well as the transportation, filling and dispensing procedures used with these chemicals are strictly regulated in the United States by the U.S. Department of Transportation (DOT). Such equipment and procedures are subject to regulatory regimens in other countries as well.
The valves used in filling and dispensing from such containers are designed to be operated manually. Therefore, the attendance of an operator who is properly equipped, trained, and certified is required for hooking up and disconnecting the container for the filling and dispensing operations. The containers are, however, routinely left unattended for extended periods of time while connected to the process piping during filling and dispensing. Indeed, the chemicals in these containers are typically employed in applications requiring very low dosage rates (e.g., in ratios of the chemical to the treated fluid measured in a few parts per million). Thus, it may take days, weeks, or even months for the contents of such containers to be completely discharged.
If there is any leakage at the filling/dispensing valve or downstream from it during the filling or dispensing operations, the toxicity of the chemicals involved will usually preclude the approach of an operator or technician without protective breathing apparatus and protective clothing. Therefore, some mechanism is needed for promptly closing the valve, either from a remote location, or automatically in response to the leak. This is especially true for many small water treatment sites that employ pressurized chlorine cylinders, because such sites are not regularly staffed by a skilled technician, and they are often located in or near residential neighborhoods, in which an unabated toxic chemical leak can have disastrous consequences.
The approved containers and filling/dispensing systems for the storage and distribution of toxic chemicals (particularly chlorine, sulfur dioxide, and related chemicals) fall into two general categories, based on container capacity (measured by weight): (a) Bulk shipping containers for tanker trucks (typically about 17 tons or 15,000 kg), rail cars (typically 50-90 tons or 45,000-82,000 kg), barges (up to several hundred tons or several hundred thousand kg), and stationary vessels (typically about 25-200 tons or 23,000-182,000 kg); and (b) smaller "application" containers that are easily transportable to an application site, including "cylinders" ranging from about 50-150 lb (23-68 kg), and "tons", containing 2000 lb (900 kg).
Currently, two basic types of systems are in use for the remote or automatic operation of the valves of the bulk containers. A first such prior art system employs a battery-operated actuator that is designed specifically for rail car tank valves. In this system, a battery, a motor, a gear reduction assembly, and the manual and electronic controls are installed in a single enclosure that sits astride the valve within the armored dome of the tank car. The entire system typically weighs about 60-80 lb. (27-36 kg), and it is specifically designed for the rail car tank valves. Because of its large size and the specialization of the design for rail tank car valves, this system is not suitable for use with the valves of the smaller application containers.
The other major type of prior art system, also especially adapted for rail car tank valves, employs a compressed air-driven valve actuator, which must be removed from the valve to operate the valve manually. Like the previously described system, it is not suitable for use with application container valves. Moreover, compressed air requires dehumidification and filtering to avoid freezing, corrosion, and particulate contamination, all of which can damage the system or cause it to malfunction. Such systems typically also require some mechanism for converting electrical signals to pneumatic signals, and vice versa. Accordingly, compressed air systems are typically quite complex, bulky, and expensive.
Both of the above-described prior art valve actuation systems may be operated either to open or close the valve. Accordingly, inadvertent operation of the system to open the valve when it is not safe to do so is possible.
The need has therefore been recognized for a valve actuation system that provides for emergency automatic, remote shut-off of a valve that can be opened only manually. A system that performs an emergency shut off function for bulk container valves is described in an article entitled "Emergency Shut Off Facilities for Tank Car & Tank Truck Transfer of Chlorine" (Pamphlet #57), published by the Chlorine Institute, Inc., Washington, D.C., in 1989. This system does not operate on the filling/dispensing valve, but rather requires a separate, pneumatically-actuated valve downstream from the filling/dispensing valve. By appropriately scaling down the size of the system's components, this system has been adapted for use with application containers. A disadvantage of this type of system is that it may not be adequately responsive to leaks that occur upstream from the emergency shut-off valve, and particularly at the filling/dispensing valve, which is an area of primary concern for leakage, due to the manipulation of the filling/dispensing valve and its associated fittings whenever a container is replaced. Another disadvantage stems from the possibility that, after the actuation of the emergency shut-off valve, the filling/dispensing valve may be manually closed. Where the system is used for a cryogenic liquid, this circumstance may lead to the trapping of the cryogenic liquid between the two valves without room for expansion, thereby possibly leading to an unsafe condition.
An automatic valve actuation system for closing the filling/dispensing valve of an application container is disclosed in U.S. Pat. No. 4,647,007--Bajka. This system includes a rotary valve actuator that is selectively engaged with and disengaged from an electric motor drive train. Disengagement is accomplished by the axial movement of a hand lever or wheel attached to an extension of the valve stem. Once a mode of operation, either manual or automatic, is selected by the operator, the alternative mode is effectively disabled. Should the manual mode be selected and the system left unattended, emergency shut-off in the automatic mode would not be possible.
In summary, the automatic or remote gas valve actuation systems representing the current state of the art suffer from one or more of the following shortcomings:
(1) The system is not adaptable (by virtue of size or design) to installation on application containers (tons and cylinders);
(2) The system is not serviced by an uninterruptable power supply that can be easily replenished from a readily available source, such as a 110 volt AC power supply;
(3) A compressed air source is required for pneumatic actuation, thereby adding to the cost and complexity;
(4) The manual mode of operation is disabled or interfered with;
(5) A reliable, automatic mechanism for returning from the manual mode to the "armed and ready" emergency automatic mode is lacking;
(6) The emergency shut off valve is located downstream from the filling/dispensing valve, and thus may be less than optimally responsive to leaks at the filling/dispensing valve and its associated fittings, and/or the downstream location may make the system prone to gas trapping between the filling/dispensing valve and the emergency shut off valve; and
(7) The system may be inadvertently operated to open the filling/dispensing valve automatically.
There has therefore been an as-yet unfulfilled need for an emergency gas valve shut off system that has none of the above-listed disadvantages, and yet that is economically manufactured and easily installed and used.